This invention relates to an automatic system for sequentially filling a plurality of slab-gel holders with a coagulable or polymerizable gel solution having a continuous variation in density to provide a gel having a density gradient along its height. The gel is useful as a standard medium in the analysis of proteins by two-dimensional electrophoresis to form two-dimensional protein maps. More particularly, the invention relates to an automatic system for filling the slab-gel holders to control gel variation between gels in a plurality of slab-gel holders and for automatically indexing or advancing from one slab-gel holder to another holder as each holder is filled.
The gels are used for electrophoresis separation of proteins for protein analysis and identification. The procedure begins with the isoelectric separation of protein species along a thin, elongated or spaghetti-like gel medium. In this original separation, the proteins migrate to a previously established pH point within the gel at which the sample is electrically neutral. These separations are quite well known and can be followed by a second dimensional electrophoresis separation to provide a high resolution of protein and protein subunits. In the electrophoresis separation, sample protein species migrate through a gel acting as a sieve to a point determined by their molecular weight.
The initial isoelectric separation and the second electrophoresis separation are both described in the assignee's U.S. Pat. No. 4,088,561 issued May 9, 1978, entitled "Apparatus for Electrophoresis Separation." This patent is expressly incorporated herein by reference. The electrophoresis separation is performed across an acrylamide gel containing sodium dodecyl sulfate (SDS) employed to negate the proteins' intrinsic charges. Gel compositions are well known and include polymerizable monomers as well as cross linking agents, catalysts and iniators, along with a gel buffer. Apparatus associated with the filling operation are described in assignee's U.S. Pat. No. 4,169,036.
In the past, the slab-gel holders have been filled manually in a batch-wise manner. This has required considerable effort in controlling gel variation between batches of gels to provide a plurality of standard gels. The production of standard gels is important not only for the accuracy of the protein analysis at a particular laboratory but also to control variation in standard gels at different facilities to provide results which may be transferred between those facilities.
Accordingly, one object of this invention is to provide apparatus for sequentially filling a plurality of slab-gel holders not limited to a fixed batch size. Another object of the invention is to provide apparatus for automatically controlling the filling operation and for transferring the filling apparatus from holder to holder. Another object is to provide a mechanism for quickly computing and producing one or a series of new gradient formulations for test and optimization. These and other objects will become apparent from the following detailed description.